1. Technical Field
The invention relates to demand regulators for breathing installastions of the type having a breathing gas supply inlet and a connection outlet for connection to a breathing mask, which are placed in communication by means responsive to the pressure prevailing in a control chamber connected to a zone at a reference pressure by restriction means and to the connection outlet by a pilot valve controlled by the pressure prevailing at said connection outlet.
The invention is particularly suitable for use in breathing installations for aircraft crew members whose gas supply source is a generator of oxygen enriched air operating in open circuit and using selective adsorption of oxygen on a material such as a molecular sieve and subsequent oxygen release. Sources of this type are known and frequently designated by the abbrevation OBOG or OBOGS. As compared with liquid oxygen converters, they have the advantage of not requiring a ground supply of liquid oxygen.
On the other hand, while liquid oxygen converters and pressurized oxygen cylinders delivery oxygen at a high and relatively constant pressure (the range of pressure of variation typically being in the ratio of 1 to 2), open circuit generators supply breathing gas at a low and very variable pressure. The generators typically intake air delivered by the compressor of a jet engine and the pressure varies greatly depending on the flight configuration. A generator which may be considered as representative delivers breathing gas at a relative pressure (pressure above atmospheric) likely to vary from 200 mbars to 4 bars, namely in a ratio of 1 to 20. At the minimum pressure of 200 mbars, the regulator must be able to deliver a stabilized flow of about 100 1/min.
2. Prior Art
There exist regulators of the above-defined type, whose pressure responsive means have a diaphragm forming a main piloted valve. While of small size such valves are able to deliver the flow required when the source pressure is high and exhibits small variations only. Such is not the case when the supply pressure is low and very variable. The characteristics (external diameter, diameter of the circle of contact with the valve seat, thicknress, hardness) of the elastomer diaphragm forming the pressure responsive means are selected for supporting the maximum supply pressure without excessive deformation. A diaphragm valve thus dimensioned cannot deliver the required flow rate at a low pressure. If attempts are made to adapt the membrane valve to the lowest pressure, so that it is able to deliver the required flow, there is a risk of excessive deformation under high pressures and of parasitic vibrations detrimental to efficiency and reliability.